Double-sided pressure-sensitive adhesive tapes are known. Typically they comprise two adhesive layers adhered to opposite sides of a backing which may itself comprise several layers of material.
Several techniques for the manufacture of composite pressure-sensitive adhesive tapes are also known. One technique comprises a multistep solvent coating process. Another comprises a multistep hot melt coating process. In each of these techniques the individual layers that make up the composite tape are applied sequentially. Consequently, the techniques are time consuming and labor intensive. Solvent coating processes further necessitate the use of special handling and equipment so as to minimize hazards to workers and the environment. Both processes subject the tape to severe operating conditions during its manufacture (for example elevated temperature, solvent atmosphere, etc.), thus necessitating use of non-extensible, tear-resistant, heat-resistant, and/or water resistant backing materials so as to withstand the rigors of the manufacturing process. However, this tends to limit the use of polymeric materials as the backing material to those that are oriented and/or are sufficiently thick to withstand the rigors of the manufacturing process.
An attempt to reduce the number of steps in the process involves the use of coextrusion. Such techniques are described in a number of publications. For example, U.S. Pat. No. 3,415,920 (Lee et al.) discloses the manufacture of a polyolefin-encapsulated adhesive fiber by the coextrusion of an adhesive and an outer skin of polyolefin. Japanese Patent Publication No. JP-46-21120 (Hori et al.) discloses a process for the melt extrusion of a stream of thermoplastic synthetic resin and a stream of an adhesive, guiding the two streams of resin through a single die to form a single fluid flow having separate layers made up of each stream, and forming a tape having adhesive on one side. U.S. Pat. No. 3,823,211 (Colombo) discloses a method of coextruding a synthetic foam/synthetic resin backing construction.
It is also known that a multilayer polypropylene film can be prepared by coextrusion and that an adhesive can be subsequently coated onto the multilayer film.
U.S. Pat. No. 4,379,806 (Korpman) discloses producing a two-layer pressure-sensitive adhesive tape. In one process a tacky, thermoplastic rubber/resin pressure-sensitive adhesive and a backing of a normally non-tacky thermoplastic resin are coextruded to provide a tape having adhesive on only one side. In another method a blown layered film of the backing and adhesive is extruded. The film is then collapsed so that the backing film is joined to itself. The adhesive and the backing each have a torque value of between about 100 meter grams and 1000 meter grams when worked at 74 revolutions/minute (RPM) at 420.degree. F. in a Brabender torque dynamometer. Additionally, the adhesive is joined to the backing "through an intermediate interlocking layer formed by controlled penetration of components during coextrusion of the film-forming and the adhesive compositions" (column 2, lines 3-7).
U.S. Pat. No. 4,888,075 (Freedman) discloses an all plastic multilayer liner and facestock for pressure-sensitive labels, tapes, etc. and a method of making such liners and facestocks. The liner/facestock is coextruded from any suitable coextrusion die such as, for example, a Cloeren "vane" die (column 2, lines 56-61). The pressure-sensitive adhesive is subsequently applied to the liner/facestock either by adhesive transfer from a release liner (column 6, lines 14-22), or in a subsequent coating step (column 6, lines 23-29 and FIG. 3A).
European Patent Application Publication No. 0 411 820 A1 (Wood et al.) discloses a reinforced pressure-sensitive adhesive tape and a method of making the same. The tape comprises a backing having a plurality of ribs at least partially embedded in one of its major surfaces. A pressure-sensitive adhesive is provided on at least one surface of the backing. The backing and reinforcing ribs can be coextruded together followed by application of the adhesive.
There have also been attempts to coextrude multilayer two-sided adhesive tapes directly into a nip formed between two solid surfaces. This technique has not been entirely satisfactory as the pressure on the extrudate while it is in the nip causes the adhesive to aggressively adhere to one of the surfaces. Once adhered, it is difficult to remove the adhesive.
While the tapes of these prior efforts are useful, their manufacture and conversion into an adhesive tape generally involves a series of sequential operations or extra handling which add to the cost and complexity of their preparation. The tapes disclosed in the above-mentioned publications have adhesive on only one side. To the extent that they disclose a tape having adhesive on both sides, they do so only through a multi-step process, rather than one in which the entire tape is produced via a single melt processing step.
Adhesive tapes with pressure-sensitive adhesive layers on two sides, typically with a backing between the adhesive layers, typically referred to as double-sided adhesive tapes, have been known. Typically the adhesive layers are substantially coextensive. In some instances, however, while one adhesive layer is coextensive with the backing the other adhesive layer is smaller such that a portion of the backing is exposed. In this manner the backing provides finger tab. Such tapes have been used as closures on diapers and personal hygiene articles. Such tapes are manufactured through sequential coating processes and so-called "zone coating" techniques.